npj Microgravity最新文献

This study reports a new method of analysis to measure the surface tension of high melt-temperature liquid metals using levitation in microgravity. The method, which leads to a self-consistent benchmarking technique to determine surface tension, requires forced oscillations of a levitated drop until the drop responds by deforming at a target mode, say the first fundamental mode of the natural frequency of the drop. Decomposition of the drop shape into Legendre modes, followed by time-domain analysis, reveals that the response to a target-mode forcing is composed of multiple modes that oscillate at frequencies, commensurate with the natural frequencies of those modes. We refer to the multiple modes that emanate from the target mode forcing as subordinate or ancillary modes. This then means that multiple modal shapes constituting the deforming drop's response co-exist. It is found that the ratios of the experimentally determined ancillary modal frequencies correlate well with the theoretical ratios predicted by the Rayleigh formula, thereby providing a self-consistent benchmark method for surface tension determination for any given sample, regardless of its composition. Validation of this method has been performed using experiments on the Electrostatic Levitation Furnace (ELF) in the KIBO module aboard the International Space Station (ISS) demonstrating accuracy and precision.

Airborne transmission is one of the most efficient routes of respiratory viral spread, posing a significant challenge in controlling major infectious diseases such as COVID-19. In microgravity environments, such as the International Space Station (ISS), this mode of transmission requires heightened vigilance and preventive measures due to the prolonged suspension of virus-laden particles, which increases the risk of infection. Using the COVID Airborne Risk Assessment (CARA) tool, we assess the risk of airborne transmission of respiratory viruses, using SARS-CoV-2 as a case study, in microgravity by simulating the emission, dispersion, and inhalation of virus-laden particles. Our simulations show that the unique conditions of microgravity allow these particles to remain airborne for more extended periods compared to Earth, leading to a 286-fold increase in virus concentration in the air and resulting in nearly twice the probability of infection for a susceptible host. We also evaluated the effectiveness of preventive measures. We found that facemasks could reduce the risk by up to 23%, while continuous HEPA filtration at five air changes per hour proves crucial for managing air quality and minimizing infection risks by reducing airborne virus concentration by 99.79%. To explore potential effects of spaceflight-induced immune suppression on transmission risk, we modeled hypothetical scenarios with increased viral shedding based on herpesvirus reactivation data. An 8-fold increase in viral load (as observed for herpesviruses in space) raised infection probability by 12 percentage points above baseline. Sensitivity analysis with 4-fold and 16-fold increases showed infection risk scales proportionally with viral shedding intensity. Although facemasks and air filtration help mitigate the risk, their effectiveness diminishes when viral load is elevated. Enhancing host immunity through vaccination or other interventions is vital, potentially reducing infection probability by up to 14.17% when combined with HEPA filtration.

This pioneering study investigated cardiovascular responses in children during simulated microgravity exposure using a 15° head-down tilt (HDT) for one hour. Twenty-six healthy participants aged 8-14 years (15 girls, 11 boys) underwent continuous non-invasive monitoring of nine cardiovascular parameters, including heart rate, stroke volume, cardiac output, and blood pressure. Results showed that children tolerated HDT well, with no signs of distress or adverse reactions. Heart rate decreased significantly during tilt, while stroke volume and left ventricular ejection time increased, suggesting adaptive cardiovascular adjustments similar to those observed in adults under microgravity conditions. Cardiac output and cardiac index exhibited transient rises in girls, followed by normalization, and no significant intersex differences were found in blood pressure responses. These findings indicate that children display physiological adaptability comparable to adults, providing novel insights into pediatric cardiovascular function in microgravity analogs and supporting considerations for future inclusion of young participants in space research and tourism.

This review provides a comprehensive analysis of acceleration mechanisms utilized in air-breathing electric propulsion, focusing on their fundamental principles, advantages, and the latest technological advancements. These thrusters, which utilize atmospheric gases to generate plasma and produce thrust, hold significant promise for very low Earth orbit missions due to their potential for high-efficiency propulsion. Central to their operation are the different mechanisms of acceleration. The review systematically categorizes the various acceleration mechanisms and discusses the physical principles behind these mechanisms, their integration into air-breathing propulsion architectures, and recent experimental efforts aimed at performance optimization.

Spaceflight acutely but transiently elevates intraocular pressure (IOP), often attributed to cephalad fluid shift and choroidal expansion. We propose that anterior segment mechanics, including lens-iris diaphragm position and conventional outflow loading, may contribute to early IOP changes. Comparing phakic and pseudophakic eyes, paired with anterior segment OCT and complementary imaging aboard the International Space Station, could define mechanisms and inform astronaut screening and ocular risk mitigation.

Unlike earlier short-duration lunar missions, current exploration-class missions include extended periods of microgravity exposure prior to lunar surface operations. Current exercise systems on the International Space Station are bulky and power-intensive, limiting their applicability for deep space missions. The European Enhanced Exploration Exercise Device (E4D) addresses these constraints by combining aerobic and resistive exercises in a compact, multifunctional device. This study compared kinematics and perceived exertion between exercises performed on E4D's unpowered mode and conventional gym equipment. Fourteen participants performed rowing, seated row, deadlifts, and bench press under both conditions while wearing a sensor-based motion capture system. Differences in joint angles, angular velocities, and perceived exertion were observed, likely influenced by variations in ergonomics, force production mechanics, and load distribution. Whilst differences were significant, full-body aerobic and resistive exercises were possible using a single device without a motor to generate resistance, relevant for missions with volume and power constraints.

Spaceflight-induced cardiac atrophy and rhythm disorders are linked to dysregulation of the adrenergic-cAMP-PKA pathway. Gravity-dependent alterations in adrenergic signaling, particularly cAMP dynamics, remain poorly understood. Using fluorescence biosensors, we studied intact cells under simulated microgravity and hypergravity. We observed shifts in the EC50 of cAMP production: leftward under hypergravity and rightward in microgravity, with faster cAMP accumulation kinetics in hypergravity. Cytoskeletal remodeling, hypothesized to be a determinant of such changes, was negligible, suggesting alternative mechanisms. These findings highlight significant gravity-induced offsets in the pharmacology of a prototypical G protein-coupled receptor, with implications not only for adrenergic signaling but also for other pathways of pharmacological interest, potentially informing countermeasures for astronaut health and pharmacology in altered gravity settings.

Microgravity alters key biological processes, impacting cellular structure, function, and metabolism. In the absence of gravity, cells experience changes that disrupt signal transduction, gene expression, and metabolic pathways, affecting growth rates and cellular viability. Ground-based simulators like clinostats replicate microgravity conditions to study these effects, allowing researchers to examine cellular responses in the lab. This study uses Saccharomyces cerevisiae to explore microgravity's impact on yeast metabolism and properties. Yeast cells are exposed to simulated microgravity via a 2D-clinostat and analyzed using dielectrophoresis over 1-24 h. A double-shell model reveals significant morphological and membrane changes under these conditions. Results indicate notable differences in membrane permittivity and conductivity, with microgravity reducing the folding factor in yeast cells, impairing nutrient uptake and energy production. This research enhances the understanding of microgravity's effects on eukaryotic cells and contributes to the field of gravitational biology.